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?atented Oct. 28, 1930 iJNlTED STATES PATENT OFFICE,

ERWIN MANKENBERG, 0F BERLIN-TREPTOW, GERMANY, ASSIGNOR, BY IYCESNE ASSIGN- MENTS, TO AGFA ANSCO CORPORATION,

BATION OF NEW YORK 01? BIQ'GHAMTON, NEW YORK, A. CORPO- PROGESS 0F DEVELOPING PHOTOGRAPHIG REV'EBSAL FILMS Ho Drawing. Application filed March 15, 1928, Serial No. 262,061, and in Germany March 25, 1927.

This invention relates to the development oi photographic reversal films, particularly of reversal motion picture film. its object is to improve the process of developing these films by substituting a uniform treatment in the dark-room for the individual treatment used up to now for different lengths of the film which are differently exposed. Such uniform treatment can be carried out irrespective of the difierences in the length of the films or the amount of exposure to which they have been subjected. It can, therefore, be done mechanically without the former necessity for careful control.

i found that the photographic reversal film can be developed, reversed and re-developed in a uniform manner without any time-wasting control and intermediate treatment between the first and second development, by omitting the usual compensation for the difi'erences .of illumination before the second development and equalizing the density of the film after reversal.

In this equalizingtreatment of the reversed picture, it is necessary in order that the silver deposit shall in no case be too thin that after the second development, which produces the positive, all the separate pictures composing the film should have sufiicient density. To ensure this in the uniform development, the film must purposely be under-d-.."-.loped in the first development. For each. film-material an under-developed constant can be determined once for all and so adjusted that even when the film has been over-exposed in taking the photograph, a positive of good density is obtained after reversal.

The invention may be carried out, for 111-.

stance, as follows :One or several series of motion-pictures are taken on a motion picture reversal film. The different series of latent images on the same film-strip are probably partly underexposed, partly overexposed and partly normally exposed. This film is then developed and reversed in a known manner. ,The duration of the first development is made the same for all exposures. Likewise the duration of the bleaching-bath and of the clearing bath as well as that of the second development can also be made the same for all exposures. Where, for example, a certain film-material has hitherto been developed with a certain developer, for ten minutes when exposure was assumed to be normal, for twelve minutes when under-exposure was assumed, and for eight minutes when over-exposure was assumed; or in case the first development was kept constant, a control and an individual equalizing treatment which could by no means he made mechanically, was adopted, now according to this invention the whole length of the film is treated without considering the character of the illumination, as f0llows':-For 6 minutes with the first developer, for et-minutes with the bleaching bath, for 2 minutes with the clearing bath, and for 3 minutes with the second developer. it is then found after the rever $211 that the diapositives have too much density which may even be a fog in under-exposed pictures and difi'ers only little from a normal positive in overexposed parts. The various pictures of the film are then treated with a silver solvent of a uniform and even reducing action for a more or less prolonged time varying according to the degree of the density of the pictures.

A suitable solvent for silver is, e. g., the mixture, known a:- a reducin bath, of the following solutions A and B in the proportion of 8 parts of solution A to 100 parts of solution B.

Solution A: 1 gram of iodine, 2 grams of potassium iodide, 200 grams of water.

Solution B: 4 grams of thiocarbamide, 100 grams of water.

The same solvent may also advantageously be used for eliminating the negative silver picture from the layer (that is to say: as the bleaching bath).

The advantages of the new process are the following: The duration of treatment of the film in the various baths is always the same, irrespective of the diflerences of illumination during exposure of the dilferent pictures composing the film. There is no intermediate control and the film can, therefore, be treated mechanically until the reversal has occurred. An examination of the film to ascertain whether and to what extent the density of the whole or of some parts thereof must be equalized, is made only after the diapos1- tive has been finished. Since the finished silver picture is examined in this case, the control is far easier than when it is'done in the dark-room where the density to be expected as the result of reducing a quantity of silver bromide must be judged. If desired, the film may be dried after the reversal and wound up and subsequently treated at any desired time, so that the positive may receive its final character after the film has been projected as an experiment. Moreover, in case the equalization of the density is not satisfactory for all individual pictures, the treatment in the silver solvent can at any time be claim:

1. In theprocess of developing photo,-

graphic films by reversal, the steps which comprise first subjecting the film to an underdevelopment, dissolving the silver image, developing the remaining silver salt image after a second exposure and'then equalizing the excessive density of the reversed image due to the first under-development by means of a solvent for silver, which is characterized by a uniform and even reducing action.

-2. In the process of developing photographic films by reversal, the steps which comprise first uniformly subjecting the film to an under-development, dissolving the .silver image, clearing and developing the remaining silver salt image after a second exre and then equalizing the excessive ensity of the reversed image due to the first under-development by means of a-solvent for silver, which is characterized by a uniform and even reducing action.

3. In the process of developing photographic films by reversal, the steps which comprise uniformly subjecting the films to an under-development, dissolving the silver image, clearing and developing the remainin silver salt image after a second exposure an then individually equalizing the excessive densities of difierent sections of the film by means of a. solvent for silver, which is char acterized by 'a uniform and even reducing action.

4. In the process of delevoping motion picture films by reversal, the steps which comprise first subjecting the film to a uniform mechanical treatment comprising the steps of under-developing the film, dissolving the silver Image and clearing and developing the re silver salt image after a second exposure an then individually equalizing the excessive densities of different sections of the. film by means of a solvent for silver characterized by a uniform and even reducing action.

In testimony whereof, I aflix my signature.

ERWIN MANKENBERG. 

